This invention relates to the field of robotics and, more particularly, to proximity sensors for robot hands, arms or other moving parts. It also relates to manufacturing methods which utilize such robots to handle magnetized objects.
The need for efficient proximity sensors for robotics has been recognized for some time. Obstacle avoidance, safety and high speed of approach are among the reasons for the usefulness of such sensors. For robotic applications various kinds of physical effects, including acoustic, optical, capacitive and magnetic effects, have been proposed to achieve the sensing function. So far, the proposed devices for robotic proximity sensors have been straightforward extensions of control or dedicated-automation devices; thus, the programmable motion of the robot has not been taken into account.
Various types of magnetic phenomena (e.g., the Hall effect, variable reluctance, magnetoresistance, Eddy currents, magnetostriction, etc.) are applicable to robotic sensors for special purposes. However, in any magnetic sensor there are a priori disadvantages: first, the obvious limitation to detection of magnetized objects (i.e., objects of magnetic material or objects of nonmagnetic material but which include a magnetic marker); second, the interference caused by extraneous magnetic fields; third, the frequent presence of hysteretic effects; and, fourth, limited range of sensing. Nevertheless, magnetic sensors have found widespread use in specialized applications, for example, in the measurement of the speed of rotation of wheels and gears.
For robotic applications, the previously mentioned disadvantages can be balanced and outweighed by several inherent advantages. First, the magnetic field, being a vector quantity, contains information not only about distance but also about orientation. A trivial example of magnetic orientation-detection is the compass. Thus, magnetic sensors have inherent advantages for the critical problem of part orientation. A second critical problem in robotic manipulation is sensor fragility. A magnetic sensor, however, can be embedded in a robot hand and thus can be protected from mechanical damage. For the same reasons it can be combined without interference with other sensors, such as tactile sensors. Finally, magnetic materials are inexpensive, easy to fabricate and highly developed technologically.